The ultraintense laser-plasma interaction introduces high inhomogeneity (densities and momenta) in both space and time, to the mixed plasma. These inhomogeneities lead to the excitement of broadband plasma waves. The simulations suggest instabilities, analogous to the oblique filamentation instability [1]}, [2]}, [3]}, are observed. The HHG spectrum further depends on the solid angle where the observer is deployed, because the target surface is observed to be deformed in the simulations, by both the hole-boring process and the Rayleigh-Taylor like instability [4]}, [5]} at the surface. This will be explored in future publications.
